Effect of solvents and temperature on the critical micellar concentration of sodium dodecyl sulfate and cetylpyridinium chloride

The critical micellar concentrations (cmc) of sodium dodecyl sulfate (SDS) and cetylpyridinium chloride (CPC) in acetonitrile-water media of various c ompositions hare been determined at different temperatures. The cme of sos slightly decreases,vith the increase in acetonitrile concentration and with the increase in temperature, whereas that of CPC increases,vith the increa se in concentration of acetonitrile and temperature. An attempt has been ma de to explain this type of behaviour: Contrary to the general expectation, the micellization of SDS and CPC in mixed solvents seems to be enthalpy-con trolled rather than entropy-controlled.